Method and apparatus for controlling equalizer using sync signal in digital vestigial sideband system

ABSTRACT

An equalizer is controlled using a sync signal in a digital vestigial sideband system is provided, in which the sync signal is accurately separated even though a ghost having a short delay time and a large size is generated. A switching unit is provided between a matched filter and the equalizer, which selects one of two input signals according to rejection filter on/off control signals and separates a data segment sync signal and a data field sync signal from the selected input signal. A control signal is produced via the separated sync signal to control the equalizer to operate in one of a blind mode and a training sequence mode. Since the equalizer performs sync signal separation by using the ghost removed signal, a system initial operational time becomes shorter, and accurate sync signal separation is possible even if severe ghosts occur, to thereby improve degeneration of system performance greatly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control of an equalizer in a digitalvestigial sideband (VSB) system, and more particularly, to a method andapparatus for controlling an equalizer using a sync signal in a digitalVSB system, in which the sync signal is accurately separated even thougha ghost having a short delay time and a large size is generated, andthen the equalizer is controlled with the separated sync signal, tothereby improve system performance greatly.

2. Description of the Related Art

A digital broadcasting which provides video and audio information formultimedia services is being commercialized worldwide. In digitalbroadcasting, it is very crucial to provide a modulation anddemodulation technique which can assume a sufficient bit transfer ratein order to transmit video and audio signals through a broadcastingchannel having a predetermined bandwidth. An American-oriented groundwave digital broadcasting receiver is a digital VSB system employing aVSB modulation and demodulation technique in order to assume a high bittransfer rate in a limited bandwidth. A conventional digital VSB systemis shown in FIGS. 1 and 2.

FIG. 1 is a block diagram showing a conventional digital VSB system. Thedigital VSB system shown in FIG. 1 includes a tuner/IF (IntermediateFrequency) unit 1 selecting a RF (Radio Frequency) broadcasting signalof a desired channel from an incoming signal via an antenna. Thetuner/IF unit 1 converts a selected RF broadcasting signal into an IFsignal and outputs the converted result. An analog-to-digital (A/D)converter 2 converts an IF analog broadcasting signal into a digitalform according to predetermined frequency clock oscillating in a voltagecontrolled crystal oscillator (VCXO) 3 and outputs the digital signal.The output signal of the A/D converter 2 is input to a carrier recoveryunit 5 formed of a digital frequency phase locked loop (DFPLL) and anautomatic gain control (AGC) unit 8. The DFPLL 5 which is a carrierrecovery unit corrects frequency and phase errors of the input signal byusing a pilot carrier signal, and then demodulates the corrected resultinto a baseband signal to recover the carrier. The carrier recoveredsignal is input to a matched filter 6. The matched filter 6 corrects thecarrier recovered signal of the DFPLL 5 into a signal equal to apassband predetermined in a transmission end, and removes noise otherthan the passband, to thereby play a role of heighten an accuracy ofsignals. The output signal of the matched filter 6 is input to a symboltiming recovery unit 4, an NTSC rejection filter (NRF) 7, the AGC unit 8and a sync signal detector 10. The NRF 7 receives the output signal ofthe matched filter 6 and removes an NTSC component from the receivedsignal, to thereby prevent degeneration of HDTV signals due to an analogNTSC TV signal. The sync signal detector 10 detects a data segment syncsignal from the output signal of the matched filter 6, and outputs thedetected data segment sync signal to the symbol timing recovery unit 4,the AGC unit 8, an equalizer 9 and other blocks.

Meanwhile, the symbol timing recovery unit 4 recovers a symbol timingerror from the output signal of the matched filter 6 in synchronizationwith the data segment sync signal detected in the sync signal detector10. Here, the VCXO 3 receives the output signal of the symbol timingrecovery unit 4, generates timing recovered symbol clock, and providesthe timing recovered symbol clock to the A/D converter 2 as samplingclock. The equalizer 9 equalizes the output signal of the NRF 7 insynchronization with the data segment sync signal detected in the syncsignal detector 10, to thereby remove ghost and inter-symbolinterference due to a multi-path occurring during transmission of groundwave broadcasting. In general, in the case of a digital communicationssystem, a transmission end transmits a transmission signal in which apredetermined training sequence is inserted at every interval, and areception end detects and recognizes the training sequence to therebyidentify the pattern of the transmitted signal and perform equalizing.In the case that the transmission end cannot transmit the trainingsequence together with the transmission signal, the reception end cannotsee the pattern and state of the received signal. In this case, a blindequalizing should be performed.

The output signal of the equalizer 9 is input to a phase tracker loop(PTL) 11. The PTL 11 attempts phase tracking in order to compensate fora phase error. The output signal of the PTL 11 is input a R-S(Reed-Solomon) decoder 14 via a TCM (Trellis coded modulation) decoder12 and a deinterleaver 13 in turn. The R-S decoder 14 decodes an inputsignal according to the R-S decoding and corrects an error generated ina channel. That is, the R-S decoder 14 corrects an error usingredundancy data in the case that an error occurs in original data. Theerror-corrected data in the R-S decoder 14 is input to a derandomizer15. The derandomizer 15 reproduces a data packet for packet decodingfrom the input data. That is, a part of packets selected from the datapackets are reproduced into an audio part of a digital broadcastingprogram and the other selected packets are reproduced into a video partof the digital broadcasting program.

FIG. 2 is a block diagram showing another conventional digital VSBsystem. The configuration of the digital VSB system shown in FIG. 2 issame as that of the FIG. 1 conventional digital VSB system. In FIG. 2, afrequency phase locked loop (FPLL) 51 is used as a carrier recovery unitinstead of the DFPLL 5 of FIG. 1, and is positioned in front of an A/Dconverter 2.

The digital VSB system of FIG. 2 carrier-recovers the output signal of atuner/IF unit 1 via the FPLL 51 in analog form and outputs the carrierrecovered signal to an A/D converter 2. The A/D converter 2 samples thecarrier recovered reception signal according to predetermined frequencyclock oscillating in a VCXO 3 and converts the sampled result in digitalform, to then output the digitally converted result to a matched filter6 and an AGC unit 8. Since operations of the other components are sameas those of FIG. 1, the detailed description thereof will be omitted.

By the way, since the conventional digital VSB systems perform symboltiming recovery using a data segment sync signal, and thus the systemsnormally operate after performing sync signal separation, an initialoperation time is longer. Also, since sync signal separation isperformed in front of an equalizer and thus a ghost having a short delaytime and a large size is generated, it is not possible to separate anddetect an accurate sync signal due to an influence of the ghost, whichresults in degeneration of the system performance.

SUMMARY OF THE INVENTION

To solve the above problems, it is an object of the present invention toprovide a method for performing a symbol timing recovery without using async signal, separating a sync signal in an equalizer by using aghost-removed signal and accurately controlling an equalizer in adigital VSB system by using the separated sync signal, to thereby reducean initial operational time of the system and enhance systemperformance.

It is another object of the present invention to provide an apparatusrealizing an equalizer controlling method using a sync signal in adigital VSB system.

To accomplish the above object of the present invention, there isprovided an equalizer controlling method using a sync signal in adigital vestigial sideband (VSB) system, the equalizer controllingmethod comprising the steps of: (a) selecting one of signals of thepre-end and post-end of the equalizer according to an input controlsignal; (b) separating a sync signal from the signal selected in step(a), and generating a control signal by the separated sync signal; (c)controlling the equalizer mode by the sync signal separated in step (b)and the control signal generated in step (b); and (d) performingequalizing corresponding to the controlled mode.

There is also provided an equalizer controlling apparatus using a syncsignal in a digital vestigial sideband system (VSB), the equalizercontrolling apparatus comprising: a recovery unit performing symboltiming and carrier recovery of digital received data; an equalizerperforming equalizing with respect to the output signal of the recoveryunit; a switching unit connected between the output end of the recoveryunit and that of the equalizer, for selecting one of two output signals;a sync signal separator and control signal generator for separating async signal from the signal selected in the switching unit andgenerating various control signals according to the separated syncsignal; and a mode controller for controlling a mode of the equalizeraccording to the control signals generated in the sync signal separatorand control signal generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention willbecome more apparent by describing the preferred embodiment thereof inmore detail with reference to the accompanying drawings in which:

FIG. 1 is a block diagram showing a conventional digital VSB system;

FIG. 2 is a block diagram showing another conventional digital VSBsystem; and

FIG. 3 is a block diagram showing a digital VSB system to which thepresent invention is adapted.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will be described withreference to the accompanying drawings.

A digital vestigial sideband system (VSB) shown in FIG. 3 includes anoscillator 100 generating clock of a fixed frequency, ananalog-to-digital (A/D) converter 2 for converting a received analogsignal in digital form according to the fixed frequency clock generatedin the oscillator 100, and an interpolation filter 200 connected betweenthe A/D converter 2 and a matched filter 6, for interpolating thesamples of the digital received data and adjusting a timing phase. Here,the interpolation filter 200 is controlled using the output of a symboltiming recovery unit 4. A carrier recovery unit 5 is configured by adigital frequency phase locked loop (DFPLL) which is a carrier recoveryunit based on a digital signal processing and carrier-recovers theoutput signal of the interpolation filter 200 in digital form. The FIG.3 system includes a multiplier 300 for multiplying the output of theinterpolation filter 200 by the output of the DFPLL 5, to thereby bedemodulated into a prior-to-being-VSB modulated original basebandsignal, a switching unit 400 connected between the output end of amatched filter 6 and the output end of an equalizer 700, for selectingone of the two signals, and a sync signal separator and control signalgenerator 500 for separately detecting a sync signal from the signalselected from the switching unit 400 and generating an operationalcontrol signal of each component. A mode controller 600 controls themode of the equalizer 700 according to the output signal of the syncsignal separator and control signal generator 500. Meanwhile, the FIG. 3system includes an NTSC rejection filter (NRF) controller 800 whichcontrols the on and off operations of an NRF 7 and the switching unit400. Here, the same elements as those of the conventional configurationare denoted as the same reference numeral. Also, since the otherelements which are positioned in the post-end of the equalizer 700 aresame as those of the conventional configuration, the detaileddescription will be omitted. The operations of the sync signalseparation and equalizer control in the digital VSB system of FIG. 3will follow in more detail.

In FIG. 3, the tuner/IF unit 1 selects a RF broadcasting signal of adesired channel from an incoming signal via an antenna. The tuner/IFunit 1 converts the selected RF VSB broadcasting signal into an IF formand outputs the converted result to an analog-to-digital (A/D) converter2. The A/D converter 2 converts the input IF analog signal into adigital form by using fixed frequency clock oscillating in theoscillator 100. The digital received data output from the A/D converter2 is input to the interpolation filter 200 and the AGC unit 8,respectively. The interpolation filter 200 interpolates the inputdigital received data under the control of the symbol timing recoveryunit 4, and outputs the symbol timing recovered reception data at thesame position as an original symbol position. That is, the interpolationfilter 200 interpolation-filters the input digital reception data andinserts any data having an intermediate value into every positionbetween the samples by the number of filter coefficients. Theinterpolation filter 200 selects data having one of the intermediatevalues inserted into every position between the samples according to theoutput signal of the symbol timing recovery unit 4 and outputs theselected data. The data output from the interpolation filter 200 isinput to the DFPLL 5 and the multiplier 300, respectively in order torecover a carrier. The DFPLL 5 which is a carrier recovery unit receivesthe data output from the interpolation filter 200 and judges whether acarrier signal of a desired channel to be received is accuratelyrecovered, to thereby output frequency and phase error correction valuesaccording to the judgement result. That is, the carrier recovery unit 5transmits the frequency and phase error corrected information of thecarrier to the multiplier 300 using a pilot carrier signal. Themultiplier 300 multiplies the data output from the interpolation filter200 by the error corrected information of the DFPLL 5. As a result, themodulation signal output from the interpolation filter 200 can bedemodulated into an original baseband signal accurately. The matchedfilter 6 corrects the outputs of the multiplier 300 into a signal whichis same as a passband predetermined originally at a transmission end,and removes noise other than the passband, to thereby play a role ofheightening an accuracy of signals. The output signal of the matchedfilter 6 is input to the symbol timing recovery unit 4, the NRF 7, theAGC unit 8, and the switching unit 400. The symbol timing recovery unit4 detects a timing error of the symbol generated during transmissionfrom the transmission end, and modifies the error detected result, tothen be output to the interpolation filter 200. Thus, the interpolationfilter 200 determines an accurate sampling position with respect to thesignal transmitted from the transmission end, by using the informationoutput from the symbol timing recovery unit 4. Meanwhile, the NRF 7performs filtering of the output signal of the matched filter 6 forremoving NTSC components according to an NRF on/off control signalapplied from the NRF controller 800. That is, the NRF 7 performs afiltering operation if a NRF-on control signal is applied and outputsthe signal to the equalizer 700 without performing a filtering operationif a NRF-off control signal is applied. The NRF-on/off control signalsare also input to the switching unit 400. The switching unit 400receives the output signal Xa of the matched filter 6 and the outputsignal Xb of the equalizer 9, and selects one of the two input signalsXa and Xb according to the NRF-on/off control signals applied from theNRF controller 800 and outputs the selected result to the sync signalseparator and control signal generator 500. That is, the switching unit400 selects the output signal Xa of the matched filter 6, if a NRF-oncontrol signal is applied, and selects the output signal Xb of theequalizer 700 if a NRF-off control signal is input. Since the level andpattern of the signal vary at the state where the NRF 7 operates, a syncsignal cannot be separated by using the output signal of the NRF 7.Thus, a sync signal can be separated by using the output signal Xa ofthe matched filter 6 which is positioned in the pre-end of the NRF 7except for the equalizer 700 at the NRF-on state. The sync signalseparator and control signal generator 500 separates and detects a datasegment sync signal and a data field sync signal from the signalselected in the switching unit 400 and generates various control signalswhich are necessary in other elements by using the two sync signals. Theoutput signal of the sync signal separator and control signal generator500 is input to the mode controller 600, the AGC unit 8 and the otherblocks. The mode controller 600 controls the mode of the equalizer 700by using the information output from the sync signal separator andcontrol signal generator 500. That is, the mode controller 600 controlsthe equalizer 700 to operate at a blind mode in the case of an initialsystem operation before a sync signal is separated, a Doppler ghostgeneration in which the size and phase of the ghost severely vary, andan unstable sync signal separation, and controls the equalizer 700 tooperate at a training sequence mode. The equalizer 700 performsequalizing with respect to the output signal of the NRF 7 so as to matchthe mode controlled by the mode controller 600.

In this embodiment, the mode control of the equalizer 700 isautomatically performed in the system by using the information outputfrom the sync signal separator and control signal generator 500.However, the mode control can be controlled as necessary externally.

As described above, the equalizer controlling method and apparatus usinga sync signal in a digital VSB system according to the present inventionperforms a symbol timing recovery without using a sync signal, performssync signal separation from the output signal of the equalizer, andcontrols the equalizer with the separated sync signal. Accordingly, thesystem initial operational time becomes very short. Also, even if asevere ghost occurs, it is possible to separate an accurate sync signalfrom the whole signal, to thereby enhance system performance greatly.

1. An equalizer controlling method using a sync signal in a digitalvestigial sideband (VSB) system, the equalizer controlling methodcomprising the steps of: (a) selecting one of a pre-end signal and apost-end signal of the equalizer according to an input control signal;(b) separating a sync signal from the signal selected in step (a), andgenerating a control signal by the separated sync signal; (c)controlling an equalizer mode by the sync signal separated in step (b)and the control signal generated in step (b); and (d) performingequalizing corresponding to the controlled mode.
 2. The equalizercontrolling method of claim 1, wherein said step (a) comprising thesub-steps of first performing filtering for removing National TelevisionSystem Committee (NTSC) components from the pre-end signal of theequalizer; and then selecting one of the pre-end signal and the post-endsignal of the equalizer according to an on/off control signal forcontrolling the NTSC rejection filtering operation.
 3. The equalizercontrolling method of claim 1, wherein said step (a) comprising thesub-steps of: (a1) sampling a received ground wave broadcasting signalaccording to a fixed frequency clock and converting the sampled resultto digital form; (a2) interpolating and filtering the digital convertedbroadcasting signal of sub-step (at) to thereby generate an intermediatevalue corresponding to each value positioned between the samples, andoutputting appropriate values among the intermediate values positionedbetween the samples according to a symbol timing recovered signal; (a3)correcting the frequency and phase errors of a carrier in the outputsignal of sub-step (a2), and converting the frequency and phase errorcorrected signal into a baseband signal using the error correctedcarrier; (a4) limiting a band of a baseband signal of sub-step (a3) andperforming symbol timing recovery from the band limited signal; and (a5)selecting one of the band limited signal of sub-step (a4) and the outputsignal of the equalizer, and outputting the selected signal.
 4. Theequalizer controlling method of claim 1, wherein said equalizer mode isselected from a plurality of equalizer modes, including at least a blindmode and a training mode for the equalizer.
 5. An equalizer controllingapparatus using a sync signal in a digital vestigial sideband system(VSB), the equalizer controlling apparatus comprising: a recovery unitperforming symbol timing and carrier recovery of digital received data;an equalizer performing equalizing with respect to an output signal ofthe recovery unit; a switching unit connected between an output end ofthe recovery unit and an output end of the equalizer, for selecting oneof two output signals; a sync signal separator and control signalgenerator for separating a sync signal from the signal selected in theswitching unit and generating various control signals according to theseparated sync signal; and a mode controller for controlling a mode ofthe equalizer according to the control signals generated in the syncsignal separator and control signal generator.
 6. The equalizercontrolling apparatus of claim 5, wherein said recovery unit comprises:an oscillator for generating a fixed frequency clock; ananalog-to-digital (A/D) convener for converting a received analog signalinto a digital form according to the fixed frequency clock generated inthe oscillator; an interpolation filter for generating intermediatevalues corresponding to signals positioned between the samples of thedigital reception data applied from the A/D converter and outputtingappropriate values among the intermediate values positioned between thesamples under the control of the symbol timing recovery unit; a carrierrecovery unit for correcting frequency and phase errors of the outputsignal of the interpolation filter and recovering a carrier; amultiplier for multiplying the output of the carrier recovery unit bythe output of the interpolation filter; a matched filter forsignal-matching an output signal of the multiplier; and a symbol timingrecovery unit for receiving the output signal of the matched filter andperforming the symbol timing recovery, to thereby control theinterpolation filter.
 7. The equalizer controlling apparatus of claim 6,further comprising a NTSC rejection filter (NRF) connected between thematched filter and the equalizer, for performing filtering in order toremove NTSC components from the output signal of the matched filter. 8.The equalizer controlling apparatus of claim 7, further comprising a NRFcontroller for controlling the NRF to be turned on/off.
 9. The equalizercontrolling apparatus of claim 8, wherein said switching unit receivesthe output signals of the matched filter and the equalizer and selectsone of two input signals according to the NRF on/off control signalsapplied from the NRF controller to then be output to the sync signalseparator and control signal generator.
 10. The equalizer controllingapparatus of claim 9, wherein said switching unit selects the outputsignal of the matched filter when the NRF is operation, and selects theoutput signal of the equalizer when the NRF is not operating.
 11. Theequalizer controlling apparatus of claim 10, wherein said sync signalseparator and control signal generator separates a data segment syncsignal and a data field sync signal from the signal selected from theswitching unit.
 12. The equalizer controlling apparatus of claim 5,wherein said mode controller controls the equalizer to operate in ablind mode when a ghost generation is determined or when a sync signalseparation is unstable is determined from the control signals producedfrom the sync signal separator and control signal generator, and tooperate in a training sequence mode in the other cases.